Arrangement in electric switch stations



1957 H. FORWALD ARRANGEMENT IN ELECTRIC SWITCH STATIONS Filed Sept. 21,1954 WWW F r O O JLO U WW H VO MM v mfi United States Patent ARRANGEMENTIN ELECTRIC SWITCH STATIONS Haakon Forwaid, Ludvika, Sweden, assignor toAllmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, 2 Swedishcorporation Application September 21, 1954, Serial No. 457,327 Claimspriority, application Sweden October 22, 1953 4 Claims. (Cl. 31759) Thepresent invention concerns an arrangement in electric switch stationswith air blast circuit breakers, in which the voltage insulation isnormally achieved at the power interrupting gap by maintaining asufficiently high pressure between the contacts of the circuit breaker,when these are opened. In circuit breakers of this kind the opening ofthe breaker is generally achieved by the action of compressed air on apiston, which, counteracted by a spring, separates the contacts of thepower breaking gap from each other. This spring is so dimensioned that asufficient contact pressure is maintained between the contacts, when thebreaking gap is closed. In plants of the above mentioned kind thecircuit breaker or breakers may be provided with rapidly workingdisconnecting switches, but in all cases disconnecting switches arearranged in the neighbourhood of the circuit breakers, by which thebreakers can be separated from the network. These latter disconnectingswitches are generally manually operated and so arranged that they areclosed independent on the fact that the circuit breakers are opened orclosed.

The above mentioned way of operating the movable contacts in the circuitbreakers will generally give a simple and reliable operation of thebreakers, but it is also followed by the disadvantage that if, due tosome reason, the pressure in the circuit breaker should decrease orentirely disappear, the contacts of the load breaking gap are closed.Such an unintentional closing of the breaker or breakers may, however,be followed by very harmful consequences either thereby that certainparts of the network can be put under tension or that the circuitbreaker can be seriously damaged, it the conditions of the network aresuch that a closing of the circuit breaker is followed by a considerablecurrent rush. An extraordinary lowering of the pressure in such circuitbreakers may also be the cause to damages thereby that, when thepressure decreases, the dielectric strength of the air between thecontacts can be lowered so far at decreasing pressure that there is arisk for the ignition of an are between the contacts. Such a suddenlowering of the pressure of the breaker or the breakers might forinstance occur, if a porcelain insulator at the circuit breaker isdamaged, so that the air rapidly escapes.

The present invention concerns an arrangement for preventing damages inthe case of a failing or considerably lowered pressure in the circuitbreakers. According to the invention this is achieved thereby that, inseries with the circuit breakers, normally closed disconnecting switchesare arranged, which are opened, before the pressure in the circuitbreaker has decreased below an unallowable low value and before thecontacts of the circuit breaker have been closed. The disconnectingswitch or disconnecting switches are for this purpose provided withoperating members, which are dependent on the pressure prevailing in thecircuit breakers, so that the disconnecting switches are opened, as soonas the pressure in the circuit breakers decreases below a certain value,but are closed again, when the pressure raises over this value again.

The invention is, however, not limited to electrical plants, where thedisconnecting switches are normally closed, but it can also be appliedto such plants, where the circuit breakers are provided withdisconnecting switches, which are opened every time, when the circuitbreakers are opened, the disconnecting switches according to theinvention being blocked in opened position, as long as the pressure inthe circuit breaker is below a certain value.

The invention is most easily understood by reference to the accompanyingdrawing, which shows a form of the invention with an air blast circuitbreaker connected in series with a disconnecting switch.

On the drawing, 1 designates a compressed air container insulatinglycarried, which contains the two power breaking gaps 2 and 3, the movablecontacts of which being operated by compressed air-actuated pistonsmovable in the cylinders 4 and 5, whereas the stationary contacts of thepower breaking gaps are arranged on the leading through insulators 6 and7 inserted in the Wall of the compressed air container. Compressed airis continuously delivered to the container 1 through the pipe line 8,and the movable contacts in the power breaking gaps are operated bymeans of compressed air delivered from the pipe line 8 over an operatingvalve 9 and a junction pipe line ltl. 11 designates a disconnectingswitch operated by a pull rod 12, which is actuated, on one hand, by atension spring 13 and, on the other hand, by a piston 15 movable in acompressed air cylinder 14. The disconnecting switch 11 is held inclosed position by a pawl 16 catching a shoulder of the pull rod 12.This pawl 16 is electromagnetically operated in the way described below.

The arrangement acts in the following way. When the circuit breaker isclosed, full pressure is prevailing in the pipe line 8, whereas thevalve 9 is closed, so that the pipe line 10 is evacuated. The piston 35in the compressed air cylinder 34 will thus be in its left handposition, and the contact pair 31 is opened, because also the contactbridge St) is in its opened position. The piston 24 in the cylinder 23is, however, in its right hand position, and the spring 25 iscompressed, so that the contact pair 27 is closed by the contact bridge26. The circuit through the electro-magnet 19 is, however, open, becausethe contact pair 23 is open, when the pull rod 12 is in its lowermostposition. if, due to some reason, the air pressure in the circuitbreaker should disappear, when the breaker is closed, the disconnectingswitch remains in its closed position, because, when the piston 24 ismoved to the left and the contact pair 29 is closed by the bridge 26,still no circuit can be closed through the electro-magnet 33 due to thefact that the piston 35 holds the contact bridge 30 in its openposition. If, however, the circuit breaker is open, full air pressure isprevailing in the pipe line 3 as well as in the pipe line 19, and thecontact bridge 30 will thus hold the contact pair 31 closed, and thecontact pair 27 is closed by the bridge 26, If now, due to some cause,the pressure should disappear in the pipe line 8, the contact bridge 26closes the contact pair 29, as the piston 24 moves to the left underinfluence of the spring 25, so that a circuit is closed from plus overthe contact pair 31 and the bridge 30 and the contact pair 29 and thebridge 26 to the contact pair 22 and the bridge 21 and further throughthe coil 33, the pawl 16 then being moved to the left, so that the pullrod 12 is liberated and the disconnecting switch is opened as the pullspring 13 pulls the rod 12 upwards. As the pressure in the pipe line 10in this case disappears simultaneously with the pressure in the pipeline 8, provision must be made whereby the piston 35 moves more slowlythan the piston 24 so that the contact pair 31 remains closed until thepawl has been moved to the left. This can be readily effected, forexample, by making the spring in the cylinder 34 weaker than that in thecylinder 23. It then the air pressure in the container 1 rises again,the piston to the right, so that the contact pair 27 is closed, and nowa circuit is formed from plus over the contact pair 27 and the bridge26, the contact pair 28, the sliding contact 21 and the coil 19 for thecompressed air valve 18. When the armature 20 then is raised, the valve13 is opened, so that compressed air from the pipe line 17 flows intothe cylinder 14, and the piston 15 pulls the pull rod downwards again,until the pawl 16 catches the shoulder on the rod 12. By the arrangementof the cylinder 34 with the piston 35 it is achieved that thedisconnecting switch can be opened only when a sufiiciently high airpressure is prevailing in the pipe line 10, which means that the circuitbreaker is opened.

The invention can, of course, be modified in a plurality of ways. Thedisconnecting switch can also be operated in different manners, but inall cases the arrangement for operation must be such that thedisconnecting switch is blocked in closed position, as long as thecircuit breaker is closed, and is arranged to be opened when, at opencircuit breaker, the air pressure decreases below a certain value. Theinvention is, however, also applicable in such plants, where thedisconnecting switch or disconnecting switches are arranged to benormally opened after every opening of the power circuit breaker, andaccording to the invention the operating device for the disconnectingswitch is, in this case, such that the closing of the disconnectingswitch cannot take place, as long as an insufficiently high air pressureis prevailing in the circuit breaker. In this case the arrangement foroperation of the disconnecting switch must be such that thedisconnecting switches are closed, before the power breaking gaps areclosed.

I claim as my invention:

1. Arrangement in electric switch stations comprising 24 is moved againair blast circuit breakers having breaking contacts normally held in theclosed position, a compressed air container enclosing said contacts,pneumatic means for opening the contacts, at least one disconnectingswitch in circuit between the contacts and the station network, andmeans whereby, only when the circuit breaker is open and when the airpressure inthe circuit breaker is reduced below a pre-determined value,the said disconnecting switch is opened when in the closed position andis blocked when in the open position.

2. Arrangement in electric switch stations according to claim 1, inwhich the said means for opening the disconnecting switch operatesbefore the breaking gaps of the circuit breaker are closed. 7

3. Arrangement in electric switch stations according to claim 1,comprising means whereby the disconnecting switch is blocked in closedposition when the power breaking gaps are closed. 7

4.. Arrangement in electric switch stations according to claim 1,comprising means whereby the disconnecting switch is arranged to beautomatically closed again only when the power breaking gaps are openedwith restored air pressure.

References Cited in the file of this patent UNITED STATES PATENTS2,084,877 ,Uhde June 22, 1937 2,213,658 Thommen Sept. 3, 1940 2,235,074Kesselring Mar. 18, 1941 2,327,493 Bresson Aug. 24, 1943 2,450,628Boisseau et al. Oct. 5, 1948 2,491,945 Baker et al. Dec. 20, 19492,676,285 Jansson et al. Apr. 20, 1954

